<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <script src="../vue.js"></script>
  </head>

  <body>
    <div id="app">
      <input type="text" v-model="msg" />
      <button @click="count++">累加count</button>
      doubleCount:{{doubleCount}}
    </div>
    <script>
      Vue.config.productionTip = false;

      const vm = new Vue({
        el: "#app",
        data() {
          return {
            msg: "",
            count: 2,
          };
        },
        computed: {
          doubleCount() {
            return this.count * 2;
          },
        },
        /*
          wacth可以监听一个data属性或者一个计算属性,就会触发watch侦听的回调函数,我们可以在回调函数中做后续的事情
        */
        watch: {
          msg(newVal, oldVal) {
            console.log("发送请求", newVal, oldVal);
          },
          doubleCount() {
            console.log("重新计算了count");
          },
        },
      });
    </script>
  </body>
</html>
